With recent further increases in demand for higher capacity and lighter weight batteries, improvements in the volume ratio and reduction in the weight of batteries have been in greater demand than ever, even for battery cases that house a power-generating element. To attend to such demands, battery cases are manufactured mainly by the drawing and ironing process, by which a thin can be made with a small amount of material.
In the drawing and ironing process, a steel plate is punched into a circular blank and processed by drawing at the same time to form a bottomed cylindrical can member, and then the can member is processed by ironing to mold the blank of a bottomed cylindrical battery case (hereinafter, referred to as a “blank case”) that is thin-walled and long in the axial direction. Wavy projections (earring) are formed, due to anisotropic materials, at the opening end portion of the blank case molded by the drawing and ironing process. Thus, the earring is removed and the opening end portion is shaped by cutting the opening end portion of the blank case, so as to shorten a slighter longer blank case to a predetermined size.
FIG. 17 shows a can manufacturing device (trimmer) that is used for such cutting processes (see Patent Documents 1 and 2). A trimmer 100 shown as an example in the figure has a mandrel 102 on which a blank case 101 is fitted to position the aluminum beverage can of the blank case 101, and a main shaft 103, to which the mandrel 102 is mounted.
The main shaft 103 is connected to an external blade supporting shaft 104 via a gear and the like, so as to rotate along with the external blade supporting shaft 104. On the other hand, a toroidal internal blade 105 is provided at the proximal end portion of the mandrel 102. The internal blade 105 and an arc-shaped external blade 106 that is supported by the external blade supporting shaft 104 overlap with a predetermined clearance therebetween, and cut the case wall of the blank case 101 sandwiched therebetween in the circumferential direction.
The mandrel 102 has a hollow structure, and a plurality of suction holes are formed along the peripheral wall, and the hollow portion is connected to a suction device. By sucking air through the hollow portion of the mandrel 102 with the suction device, the case wall of the blank case 101 is suctioned onto the peripheral surface of the mandrel 102.
The above-described suction holes are opened in a plurality of strip-like grooves that extend in the axial direction and are provided at the peripheral surface of the mandrel 102, and the suctioned blank case 101 deforms in accordance with the shape of the grooves. This prevents the blank case 101 from idling with respect to the mandrel 102 while cutting.
Patent Document 1: Japanese Laid-Open Patent Publication No. Hei 10-76420
Patent Document 2: Japanese Laid-Open Patent Publication No. Hei 10-76418